ICEpower 50ASX2BTL needs preamp for guitar and cello

[xtian]

I'm creating a SS power amp for my friend, a guitar and cello player.

ICEpower 50ASX2BTL: https://www.parts-express.com/pedocs...data-sheet.pdf

I have this amp working, but lacking any preamp, it's pretty quiet with guitar. The ICEpower module offers a +-24vDC accessory power supply rated up to 200mA. I'd like to find a simple, mono preamp module, to boost the signal maybe 10-20x (i.e., from ~0.1v to 1-2v). A volume pot would be useful also. Anyone point to something useful?

[xtian]

This is a decent example of what I'm seeking, but finding one that ships from the states is a concern, with shipping taking so long lately...

https://www.amazon.com/Ximimark-Magn.../dp/B07HG37N1X

[glebert]

How about something like this? https://www.ebay.com/itm/MPJ-31805MI...bf10dccbd0a751

[xtian]

I like the looks of that, though the max input voltage is 12. Do you think I can create a voltage divider to drop my 24v source in half? Looks like pretty low current needed.

[glebert]

I like the looks of that, though the max input voltage is 12. Do you think I can create a voltage divider to drop my 24v source in half? Looks like pretty low current needed.

Probably, or you could use a zener diode and a resistor to drop it down to 12v. or less.

[pdf64]

Why not knock something together with an opamp and a bit of veroboard? A couple of zeners for the supply rails and maybe a dozen passive parts. Plenty of pedals or solid state amp input stages to borrow a building block from, if you’re stuck

[nhbassguitar]

Hm... Does BTL mode require differential input?

[xtian]

BTL is the mono, bridge mode, right? That's the module I ordered (mono) and it has only one input, signal/gnd.

[nhbassguitar]

Page 27, figure 17 shows 2 inputs with one of the input sources inverted before it's delivered to the board. At least that's what I think is meant by the "-1" gain block, the block being unity gain of course, but inverted. That's why I was sort of scratching my head. I admit I could be misinterpreting the datasheet. But if I were designing with this board for the first time, and wasn't completely certain, I'd want to have some sort of alternative to a single-ended scheme available. You can get (or create) that function on a single chip that will run on generic +/- supplies.

[xtian]

In our last episode, I popped the onboard 400mA fuse protecting the 24v aux supply when trying to power a DC buck converter and tiny 9v preamp module. I replaced the fuse, installed a different preamp module (one that's happy with 24v, and ditched the buck converter), and all was well.

In THIS episode, I tried to implement the Enable (mute) function by grounding the Enable pin. Now the amp is silent even with Enable function back to normal, and amp is drawing 90+ watts, getting very hot, with no signal applied (normally, it draws, like, 6 watts at idle). Damn!

From the datasheet, p.23: "The enable pin can enable/disable the amplifier. If the pin is left unconnected, then the level is high (+5V) and the amplifier is enabled. If the pin is pulled low (0V) externally, the amplifier will be disabled."

Did I mess up? Should I have used a pulldown resistor instead of grounding the pin directly?

[tedmich]

maybe you need to disconnect signal sense when the enable pin is grounded?

At least that's whats suggested in my modules manual:

[xtian]

maybe you need to disconnect signal sense when the enable pin is grounded?

Thank you, but my module does not have those features. https://www.parts-express.com/pedocs...data-sheet.pdf

[g1]

There is an internal resistor at the enable pin, so it should not matter that you grounded directly.
You're sure it was fine after the fuse blew? Even though they are 400mA fuses, the aux. supply is only rated for 200mA.
Any chance it is oscillation? (try grounding input)

[xtian]

There is an internal resistor at the enable pin, so it should not matter that you grounded directly.
You're sure it was fine after the fuse blew? Even though they are 400mA fuses, the aux. supply is only rated for 200mA.
Any chance it is oscillation? (try grounding input)

Yes, after replacing the fuse, and before I ever tried the Enable function, the amp was running fine. I let it "burn in" for 30 minutes or so, then packed it off to my client. Then my client tried implementing the Enable function at my direction and things went south. He shipped it back to me, I inspected it, swapped the ICEpower module with another same, left the Enable function grounded, and that ICEpower module failed within three seconds of power up.

The only connection I have to my chassis is earth ground from the AC wall service. All circuit grounds are independent of the chassis; my input and output jacks are isolated from the chassis. I can't imagine how I bricked two modules within seconds of power up. But the only added variable was grounding the Enable pin.

I'm exchanging emails with tech at parts-express, but so far he's like, "huh! let me ask around!"